Various solutions are used in the present technical field for determining the placement, arrangement of an object or signal/signal source (according to the invention, placement shall mean one-, two- or three-dimensional position and/or orientation). Determination and tracking of spatial position is a task of high significance in various fields (e.g. virtual reality devices, motion capture, robotics, manufacturing technology).
Optical position determination devices generally comprise a signal source (transmitter), a sensor (receiver) and a computer control unit. The transmitters are usually LEDs, lasers or light-reflecting elements, while the receivers are cameras, line-sensors or photodiode/phototransistor arrangements. When using line-sensors, i.e. sensors comprising one-dimensionally arranged light detectors, the data processing unit is required to process significantly less amount of data, therefore, it has a lower memory and computer capacity demand. Line-sensors are generally produced in the form of ICs. Line-sensors constrain the possible positions of a light source onto one plane, therefore, in a general case at least three of these are required for detecting the spatial position of the light source (two planes intersect each other in one line, while three planes intersect each other in one point). The number of signal sources and sensors is chosen depending on the given application, e.g. in case of a one-dimensional position determination, one signal source and one sensor could be sufficient.
Such an exemplary line-detecting optical sensor, known from WO 2010/013079 A1 is depicted in FIG. 1. The optical sensor comprises a line-sensor 16 suitable for detecting a signal emitted by a light source 11 and—arranged with a distance from the line-sensor 16—an optical imaging means 17, preferably a slot, or a cylindrical lens optically identical therewith, arranged cross-directionally to a detection line of the line-sensor 16. The light exiting light source 11 forms a strip of light through the slot onto the line-sensor 16, the detection of which by the line-sensor 16 provides data regarding the spatial placement of the light source 11. The optical sensor therefore constrains the possible positions of signal source 11 onto one (planar or curved) surface. Line-sensors 16 generally comprise pixel lines made up of light sensing pixels.
FIG. 2 illustrates the disadvantageous impacts of gaps being in line-sensors according to the prior art technology. Pixel line 20 illustrated in the lower part of the FIG. comprises square pixels 21, amongst which, due to the manufacturing technology, there are gaps also square in form. The lower the resolution, i.e. the cheaper the line-sensor is, the higher is the gap rate as compared to the width of the projected light strip.
In general, line-sensors 16 are commercially available in the form of ICs, by way of example, let us examine a cheap 64-pixel type. In this type, the width of one pixel is approx. 60 μm, with a gap width of approx. 40 μm, and having a pixel 21 height of approx. 125 μm. In a way as illustrated in FIG. 1, a light strip 22 is projected through the slot onto the pixel line 20 illustrated in the lower part of the figure, and the data relating to the spatial position of the light source 11 can be determined from the position of the light strip 22. The light strip 22 shown in FIG. 2 is represented with continuous line; while a light strip offset to the right is also represented in the figure with dashed lines. It is apparent that light strip 22 represented by continuous line covers 3 pixels and 2 gaps, while the offset light strip represented by dashed lines cover 2 pixels and 3 gaps. Accordingly, the sensing curve of the line-sensor 16 illustrated in the upper part of FIG. 2 takes up an irregular, wave-like form. This irregular, wave-like form of the sensing curve is extremely disadvantageous in terms of determining the spatial position, as it greatly degrades the accuracy of position detection.
There is another factor in addition to the above irregularity that can render the detection indefinite. If the edges of the light strip 22 fell onto gaps, the line-sensor 16 would render identical output signal to any light strip position within the range defined by the gaps.
FIG. 3 shows various cross-directional light strip light distribution curves occurring in systems used for detecting spatial position in the technical field of the invention. The light strip 22 comprises a range of essentially 100% light intensity, and on each of its two sides there is a strip-boundary transition 23 ranging from the essentially 100% illumination power to a 0% illumination power (i.e. a power not detected by the pixels 21). The light distribution curve of light strip 22 is dependent upon a number of factors, nevertheless, smaller or larger size strip-boundary transitions 23 appear on both sides of the light strip 22 in the case of each and every light distribution. If at the optical sensor a light strip position can occur, when all strip-boundary transitions 23 fall entirely onto gaps, then the above mentioned uncertain position would arise, rendering the position detection indefinite. In the graph of FIG. 2 these indefinite ranges are represented by the horizontal sections of the wave-like curve.
It is, therefore, the disadvantage of known line-detecting optical sensors—especially those with low resolution and low pixel number—that the gaps between the pixels in a pixel line—being present due to the manufacturing technology—render the detected signal uneven, indefinite and irregular, depending on the position of the light strip.